Protective effect of myo-inositol on oxidative damage of head kidney and spleen in juvenile grass carp (Ctenopharyngodon idella) induced by Aeromonas hydrophila

This study investigated the protective effect of myo-inositol on oxidative damage of head kidney and spleen in juvenile grass carp (Ctenopharyngodon idella) induced by Aeromonas hydrophila. A total of 540 C. idella (221.83±0.84) g were fed six diets with graded levels of myo-inositol 27.0(unsupplemented), 137.9, 286.8, 438.6, 587.7, 737.3 mg/kg for 10 weeks. Subsequently, a challenge test was conducted by injection of A. hydrophila and the survival rates recorded for 14 days. The results indicated that compared with myo-inositol deficiency (basal diet, unsupplemented), optimal myo-inositol supplementation decreased reactive oxygen species (ROS), malondialdehyde (MDA), and protein carbonyl contents, and increased the activities and mRNA levels of superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferased and glutathione reductase, and contents of glutathione in the head kidney and spleen after injection of A. hydrophila. Meanwhile, compared with myo-inositol deficiency (basal diet, unsupplemented), optimal myo-inositol supplementation up-regulated NF-E2-related factor 2 (Nrf2) mRNA and protein levels, and down-regulated Kelch-like ECH-associated protein-1 (Keap1) a and b mRNA levels in the head kidney and spleen after injection of A. hydrophila. These results suggested that optimal myo-inositol supplementation could protect fish head kidney and spleen structural integrity through increased antioxidative ability after injection of A. hydrophila. Finally, based on the antioxidant indices ROS content in the head kidney and spleen after injection of A. hydrophila, the myo-inositol requirement for juvenile C. idella was estimated to be 452.1 and 449.0 mg/kg diet, respectively.